An electronic circuit or electronic device that is used to generate periodically oscillating electronic signal is called as an electronic oscillator. The electronic signal produced by an oscillator is typically a sine wave or square wave. An electronic oscillator converts the direct current signal into an alternating current signal. The radio and television transmitters are broad casted using the signals generated by oscillators. The electronic beep sounds and video game sounds are generated by the oscillator signals. These oscillators generate signals using the principle of oscillation.

There are different types of oscillator electronic circuits such as Linear oscillators – Hartley oscillator, Phase-shift oscillator, Armstrong oscillator, Clapp oscillator, Colpitts oscillator, and so on, Relaxation oscillators – Royer oscillator, Ring oscillator, Multivibrator, and so on, and Voltage Controlled Oscillator (VCO). In this article, let us discuss in detail about Crystal oscillator like what is crystal oscillator, a crystal oscillator circuit, working, and use of crystal oscillator in electronic circuits.

An electronic circuit that is used to generate an electrical signal of precise frequency by utilizing the vibrating crystal’s mechanical resonance made of piezoelectric material. There are different types of piezoelectric resonators, but typically, quartz crystal is used in these types of oscillators. Hence, these oscillator electronic circuits are named as crystal oscillators.

Crystal Oscillator Circuit Diagram

The quartz crystal oscillator circuit diagram can be represented as follows:

(Electronic Symbol for Piezoelectric Crystal Resonator)

The above diagram represents the electronic symbol for a piezoelectric crystal resonator which consists of two metalized electrodes and quartz crystal.

(Equivalent Circuit Diagram of Quartz Crystal)

The above figure shows the equivalent circuit diagram of quartz crystal in an electronic oscillator that consists of resistor, inductor, and capacitors which are connected as shown in the figure.

Crystal oscillator circuit works on the principle of the inverse piezoelectric effect, i.e., a mechanical deformation is produced by applying an electric field across certain materials. Thus, it utilizes the vibrating crystal’s mechanical resonance which is made of a piezoelectric material for generating an electrical signal of a specific frequency.

These quartz crystal oscillators are highly stable, consists of good quality factor, they are small in size, and are very economical. Hence, quartz crystal oscillator circuits are superior compared to other resonators such as LC circuits, turning forks, and so on. Generally, 8MHz crystal oscillator is used in microprocessors and microcontrollers.

The equivalent electrical circuit also represents the crystal action of the crystal. The basic components used in the circuit, inductance L1 represent crystal mass, capacitance C1 represents compliance, resistance R1 represents the crystal’s internal structure friction, and C0 is used to represent the capacitance that is formed because of crystal’s mechanical moulding.

The quartz crystal oscillator circuit diagram consists of series resonance and parallel resonance, i.e., two resonant frequencies. If the reactance produced by capacitance C1 is equal and opposite to the reactance produced by inductance L1, then the series resonance occurs. The series and parallel resonant frequencies are represented by fs and fp respectively, and the values of fs and fp can be determined by using the following equations shown in the figure below.

(Series Resonant Frequency and Parallel Resonant Frequency)

Thus, the impedance is approximately equal to the resistance R1 during this condition. If the series resonant leg reactance is equal to the reactance caused due to capacitance C0, then parallel resonance occurs. Thus, the external circuit if offered a very high impedance by the crystal during this condition.

(Impedance vs Frequency Graph)

The above figure shows the graph between impedance and frequency of the quartz crystal oscillator circuit. Typically, crystal oscillators are having a frequency range from 32KHz to 200MHz.

Use of Crystal Oscillator

In general, we know that, crystal oscillators are used in the microprocessors and microcontrollers for providing the clock signals. Let us consider 8051 microcontroller for which an external crystal oscillator circuit of 12MHz is essential, even though (based on model) 8051 microcontroller is capable to run at 40 MHz (max). 8051 requires 12 clock cycles for one machine cycle, such that to give effective cycle rate at 1MHz (considering 12MHz clock) to 3.33MHz (considering maximum 40MHz clock). This crystal oscillator is used to generate clock pulses required for the synchronization of all the internal operations.

There are numerous applications for crystal oscillator in various fields and a few crystal oscillator applications are shown below:

• Application of Crystal Oscillator in Military and Aerospace

The use of crystal oscillator in military and aerospace, is to establish an efficient communication system, for the navigation purpose, electronic warfare, in the guidance systems, and so on.

• Use of Crystal Oscillator in Research and Measurement

The crystal oscillator is used in research and measurement for celestrial navigation, space tracking purpose, in the measuring instruments and medical devices, and so on.

• Industrial Applications of Crystal Oscillator

There are a huge number of industrial applications of crystal oscillator such as in computers, digital systems, instrumentation, phase locked loop systems, marine, modems, sensors, telecommunications, disk drives, and so on.

• Use of Crystal Oscillator in Automotive

Crystal oscillator is used for engine controlling, stereo, clock and to trip computer, and in GPS system.

• Consumer Applications of Crystal Oscillator

Crystal oscillators are used in many consumer goods such as cable television systems, personal computers, video cameras, toys and video games, radio systems, cellular phones, and so